1. Field of the Invention
This invention relates to graphic art and deals, more specifically, with an apparatus for positioning a tape, such as a transparent scale, adjacent to a planar surface, such as a drafting board, shadow-box or, more particularly, the ground glass located at the focal plane of a photomechanical or photostat-type camera.
2. Description of the Prior Art
The prior art discloses many devices which are mounted on a drafting board as an aid to drawing. Most prominent is a horizontal or vertical tape of fixed length which can be moved across the surface of the board, such as disclosed in U.S. Pat. No. 1,351,534. These types of appliances are mounted parallel to the edges of the drafting board and allow movement of the tape lengthwise or longitudinally and crosswise or transversely of the board. However, these former inventions do not provide for temporary attachment to the drafting board and do not allow for angular or diagonal placement of the tape. These restrictions have rendered appliances which are not adaptable for use on the ground glass located at the focal plane of photomechanical or photostatic-type cameras. Therefore, measuring images for metric quality at the focal plane requires time consuming conventional slide rule calculations or manual scaling on the back of the ground glass.